Drug interactions
Phenytoin + Simvastatin
Severity: Moderate
Phenytoin and Simvastatin: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin induces CYP3A4 and can substantially lower simvastatin concentrations, reducing lipid-lowering efficacy. The risk is therapeutic failure rather than toxicity.
What this interaction means in plain words
Phenytoin and Simvastatin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Phenytoin belongs to Central Nervous System; Simvastatin belongs to Cardiovascular.
Why it happens
CYP3A4 induction by phenytoin increases simvastatin metabolism.
What to do
Monitor lipid levels and increase simvastatin dose or switch to a statin less affected by induction, such as rosuvastatin or pravastatin.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Simvastatin
- Atazanavir + Simvastatin Contraindicated
- Clarithromycin + Simvastatin Contraindicated
- Cobicistat + Simvastatin Contraindicated
- Cyclosporine + Simvastatin Contraindicated
- Cyclosporin + Simvastatin Contraindicated
- Danazol + Simvastatin Contraindicated
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Phenytoin with Simvastatin?
MediHelp rates the interaction as moderate. Phenytoin and Simvastatin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin induces CYP3A4 and can substantially lower simvastatin concentrations, reducing lipid-lowering efficacy. The risk is therapeutic failure rather than toxicity.
How serious is the interaction between Phenytoin and Simvastatin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor lipid levels and increase simvastatin dose or switch to a statin less affected by induction, such as rosuvastatin or pravastatin.
What other medicines interact with Simvastatin?
MediHelp also lists interactions of Simvastatin with, for example, Atazanavir, Clarithromycin, Cobicistat. The full list is on the Simvastatin page.
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